1. Field of the Invention
The present invention relates to a device for generating a horizontal scanning periodic signal, more particularly, to a device for generating a horizontal synchronizing signal used in a phase alternation by line color television system (PAL-system).
2. Description of the Related Art
In the prior art, three different systems have been used as color television standards. Namely, a national television system committee color television system (NTSC-system) is employed in Japan, the United States, Korea, and the like; a PAL-system is employed in the United Kingdom, Germany, and the like; and a sequential-a-memoire color television system (SECAM-system) is employed in France, and the like.
Note, the PAL-system has basically the same configuration as the NTSC-system, but in the PAL-system, two chrominance signals are transferred so that a phase of one of the two chrominance signals is inverted by each line. This phase inversion in the PAL-system is used to correct the change caused by transmission lines, and thus saturation distortion can be extremely reduced.
In the PAL-system, the frequency of the basic clock [4.times.625.times.F.sub.SC ] (Hz) has been extremely high, and thus there are problems of large numbers of bits used for the counter and the like and a large circuit scale.
In the prior art, in order to solve these problems, an approximate equation is used instead of an original equation. When using the approximate equation, the frequency of the basic clock can be reduced as [4.times.F.sub.SC ] (Hz) which is lower by 1/625 than the above frequency of the basic clock [4.times.625.times.F.sub.SC ] (Hz), so that the bits used for the counter and the like can be reduced and the circuit can be much smaller.
However, an error between the frequency of the color subcarrier (color burst signal) obtained by the approximate equation and the exact frequency of the color subcarrier is caused, so that a change of light and darkness between the adjacent scanning lines may be caused. Therefore, when displaying an image of a small movement. e.g., an image of characters, a flicker (or dot interference) may be caused, and the quality of the display image may be decreased. Note, the problems caused in the prior art will be explained later with reference to the accompanying drawings.